Magnetron



Oct. 28, 1952 w WILLSHAW MAGNETRON Filed Nov. '7, 1946 I 3mm of Williamf m'llx/iwu/ Patented Oct. 28, 1952 MAGNETRON William Ernest Willshaw, Kenton, England, as-

signor to M-O Valve Company, Ltd., London, England, a limited company of Great Britain Application November 7, 1946, Serial No. 708,279 In Great Britain April 9, 1942 Section 1, Public Law 690, August 8, 1946 Patent expires April 9, 1962 32 Claims.

This invention relates to electron discharge devices and more particularly to vacuum tubes of the type known as magnetrons.

Magnetrons in various forms are particularly useful for generatin high frequency energy at extremely short wave length. A particular form of magnetron over which this invention is an improvement comprises a solid substantially cylindrical block acting as an anode and having plane ends perpendicular to its axis. An axial cylindrical aperture traverses the anode block for housing the axially disposed cathode. A plurality of slots parallel to the axis of the block are radially disposed and open at one end into the cathode aperture and closed at the other end. This construction is commonly known as a multi-segment multi-cavity magnetron.

An object of this invention is to improve the construction of magnetrons of the type referred to and thereby increase their overall efficiency.

Another object of the invention is to provide improved means for coupling the energy from the magnetron to an external circuit.

A particular advantage resulting from the modifications herein proposed is the adaptability of the magnetron to be coupled to various types of load circuits.

Another advantag resulting from the novel construction is a greater uniformity of resonance of the individual cavities of the magnetron.

Other objects and advantages \m'll be apparent from the following description of the invention, pointed out in particularity in the appended claims and taken in connection with the accompanying drawings in which:

Fig. l is a sectional view of a magnetron representing one embodiment of the invention;

Fig. 2 is a cross-sectional view of Fig 1 taken on lines 2-2;

Fig. 3 is a partial view in cross-section of a modification of the structure shown in Fig. 2 for coupling to a wave-guide;

Fig. 4 is a sectional view illustrating a modified structure in accordance with the invention;

Fig. 5 is a cross-sectional view of Fig. 4 taken along lines 5 -5;

Fig. 6 is a cross-sectional view of another embodiment showing the coupling to a wave-guide; and

Fig. 7 is a top view in partial cross-section of a modified structure of coupling and cavities.

In known magnetrons of the type described the function of the slots is to act as resonators for the oscillations generated. They may be regarded as transmission lines,'having one open end (namely that opening into the central aperture) and a closed end. If r designates the length or a slot (1. e. its dimension parallel to a radius of the cylinder), the slot will be resonant to oscillations whose wave-length is roughly 4r; the resonant frequency will not vary much with the depth of the slot (i. e. its dimension parallel to the axis).

It is important in such magnetrons that all the slots should be resonant to the same frequency. It is not always easy to achieve this result; partly because the resonant frequency depends on the length of the slot which is not easily controlled to high accuracy; partly because the sides of the slots (i. e. their terminations in planes perpendicular to the axis of the block) are open and may be differently related to conductors such as the discs which usually terminate the cathode at either end, or the leads to the heater by which the cathode is heated.

According to th invention in a magnetron of the type specified the sides of the slots are closed by conducting plates or discs, not integrated with the block, but connected to (preferably abutting against) the block and substantially perpendicular to its axis. When the sides are thus closed by discs, the radial slots thus formed are regarded better as wave-guides than as transmission lines, for the conducting discs prevent them from acting as transmission lines. Their resonant frequencies depend primarily on the axial depth which is about half the wavelength of the oscillations; it depends less on the radial length, so long as this is not very different from the depth. It is easier to adjust the depth than the length to a given accuracy, because all that is needed is to turn down the ends of the block, whereas the length has to be adjusted by milling, a far less accurate operation. Moreover, when the ends are turned down, all the depths naturally assume the same value, while each length has to be adjusted separately. Also the discs completely shield the interior of the wave-guide (and therefore its natural frequency) from any influence of bodies outside the sides or axial ends of the slot.

However, the problem of coupling the resonators to the load circuit now arises. It cannot be effected, as in the known construction, by loops introduced into the slots from their axial ends, for these are closed. In one method of coupling accordin to the invention, the slots, instead of being closed at their outer radial ends, open into an annular channel in the block surroundin its axis, and a path is provided whereby energy may pass from the oscillations in the channel to an output circuit outside the block. This path may be provided, for example, by a loop projecting into the channel or by a waveguide opening into it.

This embodiment of the invention, will now be described, with reference to Figs. 1, 2 and 3 Qf the drawing.

The anode block is made up of the outer ,cylindrical copper shell 5, closed at its ends by copper plates 6, and the inner copper block -i fi-tti-ng closely within it. The block-7 ,was originallysolid and cylindrical, but the recesses 8, the annular groove 9, and the central hole I10 have-beenz llmed or drilled out of it; further twelve longitudinal slots 12 of uniform width, opening into the hole In and, for most of their depth, into ,the groove 5, have been milled in it from end to end. The sides of the slots [2 are then covered by the copper rings or apertured discs 13, leaving the ends of the central ,hole .10 open. Atubular cathode 4 um shed 'i th e di c 1. i up o t e ,trally in the hole .19 v onnthe leads I] which enter through seals 1,8 inthe shell5.

fIlhe annular. ,groove 9, closed on its ,outer .side ,by the ,shell .5, constitutes an annular channel. In Iiig. 2 .the loop [9 extending into the channel from a coaxial line 28 in the shell 5 provides the coupling between the annular channel and the external circuit. In thealternative shown in Fig. ,3,. there isa taperedaperture or.couplin chamber ,a'pertureor slot .22 in th outer shell '5 through ,which ,theannular channel communicates .with a jcircularoutput wave-guide 23 closed at the far -endb t e e -d e hregm iIna' practical embodiment th following dimen- .sionsyvere chosen:

an th mbod men ane ot and t e an ula p iann nowiorm-a in-al oscillat n sys em, and iir l me Si dr. kv. the d th. an. a d

wow of rese s-ante -.dep 2h.and. ad a Width l ef l i snelemdethe desi ne depen ene e aeeeh eth .Bdktoa di t,a nroa metio z h .eeeImel-ma e ee e1 d saw v zsdid ied by e 8 1 onele. iti natha imust:loeiulin ensit ;:ro. 1 th iliewhe r sonan d d a ia en nden eeen i re i a v th mi ddeno b low h the WeY .l eeases to transmi .pscillations. However, itis not in eneral desir- .able the he d e, hei ld re onant at the :fr su noy a hi h the magn t n i d igned .t ope ate; better f eque c stab i ma b ob- 'a d i he o elr e n e ieh l rfillf eden frequeney; th heetreletie l ei eh thee onan frequency ofth slot s and the operating frequency yvill depend somewhaton theload that-the magjnetrqn 'feedfi. The analogy of a parallel tuned .oscillatorfedhby taps ntheinductor is here .use-

ful asa guide todesign. With .these principles in view, the ,system can usually be designed so th fin liii w i el o one dimension onlyi necessary to obtain substantially optimum'efiicier cy; this dimension may conveniently be the rel nmh dof .oom-

,th at the ma 4 depth of the slots. When the slots I2 are resonant at the operating frequency of the magnetron a high impedance plane will exist at the junction of each slot with the annular channel, in which case the loadimpedance energized from the annular channel will be reflected with maximum effectiveness into the slots l 2.

Referring to Figs. 4 and 5, in this modification a connection between the slots I2 and the annular channel 9 is established by radiator-loop combinations -projecting from the latter into the former. Fqrthispurpose the slots are expanded at one part, for example, by drilling holes axiallyenlargingeach slot as shown at 26; 21 are the radiators in the annular channel, 21 the loops in theexpanded parts. Other parts numbered in "Figsha and-5 correspond to those similarly numbered inthe aforesaid Figs. 1, 2 and 3.

I n apractical embodiment the expanded parts 26 are cylinders 5 mm. in diameter, extending a on t e o e d t o ihe slo t oles 28 .through'which .the loops enter ,are .,4 mm. in diameter The .unexoa d d ,Par a .3 :wide on h ou r end and 1 mm wideon' the inner end. 'ljhe whole radial length of the slot is there:- fore now ,(5,+.3.-|-1=9 place of}; mm. Br t the annular channel ,9 is now only 10 mm. in radia ,w dth. 'lhe rad a ors?! as ellas the loop 9 ach proje ts mm ,'inqo the chann .9-

In another method of coupling, illustrated in Fig. .6 ,one offal-1e slots ,LZ islextendedand opens into an out ut w r rsu de o e' eweson mount d on the she a t a tiona dope-red ePe dne-orfl conne t thesle proper into .the ,waye-g ide. 'Iheputer ends of th the sl ts la eie o d.- Eaoh lot m y leeconsidered .a .ea ity resonator. ,Qomm ni at n w th the at p e e is pre ente .brol i s t e ou e e d -.o tll a ee ifi bye e sdiid llt g anothe Ener y m y then Joe Add a y b s ula W veguid o de th aforesaid .w

uid 23- A modification whiohh s.s mereeemeleo e t .thatshow i Fi 4 is. h .w i f afi- .Here a .si sle lo 28 z n oddeedth odah a efil' ll on the outs d .of t e hloels enter into .a M. a e s ot which has an enlarged closed outerpnd' 3B, The other ,Slot 2 have simil enter-en s inora l o be reson ant at thes mefremy in entionmeill'lyiil .Q ZQJi l IQQl QlZ I .91. the lo p i o t outer. endro .a slot-inste d .o into itesielelnlfi 7 h. .,t .lea ih o he slots may b 11. ih ellameie 9 th enlar ed ndo mm- I claim:

.1 Inan electron discharge ,deyice, a cylindrical an d bl ck lay ng a cen ra chambe extends along the s iddi a gaz s th reo amen annu a c am e adjacent the oute surface thereo s id .b oels l arinss ois of Wid h extend n b ween sa d. .oneml erefor.commu 'tion therebetween and means coupled withlsaid annula h mbe fo transf rrin ene gy .ir

said devie 2. In an electron discharge device, a cylindrical an d bleek h vinaoe ntrel chambe x en a on t e l n i udin eziis th reof and .an-

odle ieh mee adi ee t iheo is ri .ihem f, said i loe e in elei o ,u Wi hlexiendn; be w n d... hami2e 1 iim ooie io ther between an .lrieensinolddia a l in..,a .s

vice for transferring energy therefrom.

3. In an electron discharge device, a cylindrical anode block having a central chamber extending along the longitudinal axis thereof and an annular chamber adjacent the outer surface thereof, said block having slots extending between said chambers for communication therebetween and means including a wave-guide opening into said annular chamber for transferring energy from said device. a

4. In an electron discharge device of the magnetron type, a cylindrical anode block having a plurality of radially extending slots of uniform width therein terminating at one end near the center of said block and opening into a central chamber, said block having an annular channel surrounding and opening into the other ends of said slots, conducting plates covering the sides of said slots whereby said slots form cavities which are closed except at said ends, and means for transferring energy from said magnetron comprising a portion of said block having an opening extending into said channel and a loop in said channel extending through said opening to the exterior of said block.

5. In an electron discharge device of the magnetron type, a cylindrical anodeblock having a plurality of radially extending slots therein terminating at one end near the center of said block and opening into a central chamber, said block having an annular channel surrounding and opening into the other ends of said slots, conducting plates covering the sides of said slots whereby said slots form cavities which are closed except at said ends, and means for transferring energy from said magnetron comprising a portion of said block having a tapered aperture opening at its narrow end into said channel and at its wider end into a wave-guide mounted on the outer surface of the block at one end and hermetically sealed at its outer end.

' 6. In an electron discharge device of the magnetron type, a cylindrical anode block having a plurality of radially extending slots therein, each of said slots having an inner open end near the center of said block and an outer open end toward the outside thereof, said block having an annular channel surrounding said slots and opening into said outer open ends, said slots having expanded portions, a coupling loop in each said portion extending into said channel, conducting plates covering the sides of said slots whereby said slots form cavities closed except at said open ends, and means for transferring energy from said magnetron comprising a portion of said block having an aperture opening into said channel and a loop in said channel extendin through said aperture to the exterior of said block.

' 7. In an electron discharge device of the magnetron type, a cylindrical anode block having a plurality of radially extending slots therein, each of said slots being closed on all sides and having an inner open end near the center of said block and an expanded portion toward the outside of said block, means for transferring energy from said magnetron comprising a portion of said block having an aperture opening into said expanded portion of one of said slots and a loop in said portion extending through said aperture to the exterior of said block.

8. In an electron discharge device of the magnetron type, a cylindrical anode block having a plurality of radially extending slots of uniform width therein, each of said slots having an inner annular chamber and extending from said de- 7 open end near the center of said block andall but one of said slots having an outer clos'edend, conducting plates covering the sides of said slots whereby said slots form closed cavities, means for transferring energy from said magnetron comprising a portion of said block having a tapered aperture opening at its narrow end into said one of said slots and at its wider end into a wave-guide mounted on the outer surface of the block 'at one end and hermetically sealed at its outer end.

, 9. In an electron discharge device of the magnetron type, a cylindrical anode block having a plurality of radially extending slots of uniform width therein terminating at one end near the center of said block and opening into a central chamber, said block having an annular channel surrounding and opening into the other ends of said slots, conducting plates covering the sides of said slots whereby said slots form cavities which are closed except at said ends, and means for transferring energy from said magnetron.

10. In an electron discharge device, a cylindrical anode block having a central chamber extending along the longitudinal axis thereof and having radially extending slots opening at their inner ends into said channel chamber, said slots having uniform width for at least a part of their radial length, conducting plates contacting the ends of said anode block at the sides of said slots whereby said slots are closed on all sides, and means coupled to at least one of said slots for transferring energy from said discharge device.

11. An electron discharge device in accordance with claim 10, wherein said energy transferring means comprises an aperture in the wall of said anode block coupled to at least one of said slots and opening into a hollow wave guide hermeti cally sealed to said block at one end and hermetically sealed at its outer end.

12. An electron discharge device in accordance with claim 11, wherein said aperture is tapered with at least two side walls thereof diverging from said resonator toward said Wave guide.

13. An electron discharge device comprising a cavity resonator, means for establishing a high frequency electric field within said resonator, said resonator having an aperture extending through a wall thereof, a hollow wave guide hermetically sealed at one end to said resonator in registration with said aperture, and means permeable to electromagnetic waves hermetically sealing the other end of said wave guide, said aperture being tapered with at least two side walls thereof diverging from said resonator toward said wave guide.

14. An apparatus for use at high frequencies comprising a cavity resonator and means for transferring electromagnetic energy from said resonator comprising an aperture in a wall of said resonator, a hollow wave guide hermetically sealed at one end to said resonator in registration with said aperture, and means permeable to electromagnetic waves hermetically sealing the other end of said wave guide, said aperture being tapered, with at least two side walls thereof diverging from said resonator toward said wave guide.

15. An electron discharge device of the magnetron type comprising a cathode surrounded by an anode assembly, said anode assembly including a plurality of cavity resonators, a metallic envelope enclosing said anode assembly and'cathode, the wall of said envelope having an aperture therethrough registering with one of said '2 cavity resonators means? coupling said one'cavity resonator with saidaapertureahollow wave: guide hermetically sealed at one endto" said envelope in; registration: with said aperture, and? means permeable to electromagnetic, waves' hermetically sealingsthe: other end' of said wave: guide .16 An electron discharge device in accordance with .claim 15, wherein said aperture: is tapered; with; at,- least two side' walls: divergingfrom said oneresonator tbwardsaid" waveguide.

17. An electron discharge device of the mag' netron: type comprising. anenvelope of conducting; material containing acylindrical anode block having: a} central chamber extending. along" the longitudinal? axis thereof and a: plurality ofradially. extending slots of: uniform width opening" at their inner ends into-said central cha-mber said envelope having. an aperture therethrougn regis teringz with the outer endof one of said slots;- means; for coupling said one. slot. electromagnet ically" with said aperture, and an output Waveguide:- sealed atone end t'o' said envelope in re'gistration with: said aperture: and having' means permeable: to electromagnetic waves sealing the other end: thereof.

18; An: electron discharge device according to claim? 17;, wherein said aperture is bounded by side: wallswhich diverge toward the: outside of said envelope;

19. An electron discharge: device including a cathodei and an anode block having a central chamber, said cathode being within said chamber" said anode block havingl aplurality "of T radially-extending slots of uniform-width communicating. with the chamber betweenv the cathode and: the; anode block and forming" resonators, the end: of one'ofr said slots remotefrom said cathode opening: into a: coupling chambei havingside; walls diverging" towardi the outside of said anode block, and a tubularoutputlead exten'ding from. said block and openinginto said coupling chamber.

20; An electron:v discharge device includingan anode block, said anode block beinglprovidedi with a central chamber and'havinga plurality of radially-extending slots of: uniform width oomniunieating withsaid chamber, a cathode mounted within-said chamber, the endof one -of said slots remote: from: said' cathode opening into a coupling: chamber having' side wallsi-diverging toward the outside'of said anode block, a tubular output;

lead: extending from said block" and having one endzope'ning intorsaid coupling chamber'and hav 'ing; itsother: end sealedbya closure member-per mfeable 'to electromagnetic Waves;v

21. An electron discharge device including a cathode and an? anode' block having: a: central chamber,. said: cathode: being within: saidi chain ben; said' anode-block having. a plurality ofr-a'dially extending; slots of' uniform Width communieating with the chamber between the: cathode and'the anode' block and forming resonators,- the anodeblock, said'anode blocki being provided with a central chamber fand havin'g a pluraiityof'radi ally; extending. slots :of uniform width: comm'uni eating; with .said: chamber, a: cathode mounted within said chamber, the end of one iof said slots remote from.- said cathode; being: coupled elec- 8-, tromagnetically' with a coupling-' chamber havingide walls-diverging; toward theoutside' of said anode block, a tubular output lead extending fromsaid block and having one endopening into said coupling chamber and having its other end sealed by a closure member permeable to electromagnetic waves; v

23. A high-frequency oscillator comprisingta'ri electron discharge tube having a plurality of pri mary cavity resonators therein; and a secondary cavity resonator opening into and adapted to-lieexcitedfrom said primary'cav-ity resonators; said primary cavity resonator-s being spaced with re"- spect-to each other whereby in-phaseoscillatory energy therefrom entersinto said secondarycavity resonator ata-plurality'o'f points spaced alongthe same.

24. An electron dischargedevice comprisingt'a cathode; ananode; saidanode havingapluralityof 'groovestherein and an electron receiving portion intermediate each pair of adjacent-grooves: saidgrooves constituting primary cavity resonaftors; and a secondary cavity resonator opening into and adapted to beexcited-f'rom said primary cavity-resonators.

25. An electron discharge device comprising: a cathode; an anode; said'anodehaving a plurality of 'groo'vestherein and an electron-receivingbOr tion intermediate each pair of adjacent grooves; said grooves constituting piimary'cavity' resl'i'na tors; and a secondary cavity resonator opening into and adapted to beexcited from said primary cavity resonators; said primary cavity resonat'orsbeing spaced with respect to eachother; whereby" in phase oscillatory energy therefrom entersinto said secondary cavity resonator at" a plurality of points spaced" along theisam'e.

26.- A- high frequencyoscillator' comprising an electrondischarge-tubehavingapluraiity of pr?- m'ary' cavity resonatorstherein; and asecondary cavity resonator directlycoup'led' to-and' adapted to be excited from-saidpriinarycavity-resonators:

27*. A-high-frequeneyioscillator comprising: an electrondischarge tubehaving' a plurality ofp'ri mary cavity resonatorsftherein, anda secondaryc'avity'resonator directly,- coupled to and adapt 'd" to be excited from saidfprimary ca'vity' reso v tors; and' n eans coupledtofsaid secondary'cavity resonator'for leading oscillator energy outi'of' the same:

28. Air electron discharge devicecomprising'r a". cathode: ananode; said anode including a block ofcbnducting material provided withl a central bore receptiveof-i said cathode; said block includ ing a plurality of slots" extending from said cen-' tral bore tothe exterior Wall thereof to form a plurality ofelectron-receiving'portionsiseparated by a pluralityoi" primary cavity resonators? and" annular-channel means connected to said block and cooperating with said exterior wail to" form a secondarycavity resonator; said primary cavity" resonators opening int'o' said secondary cavity resonator.

29. A n' electron discharge device coinpr'isingt a cathode; an anode; said anode includingiai block; of conducting material provided with a centrarbore receptive-0f said 5 cathode? 'saidblock'f including plurality of slots" extending" from said. central boreto t-he exterior wall thereof toforr'n a plurality of electron-receiving portions?- separated by a plurality'of'primary cavity-res" onators g and annular channel means connected to said block and cooperating with said 'exterior wantc: fori'n -a secondary cavity resonator; saidprimanyrcavityresetraters opening into'said sec ondary cavity resonator at high impedance planes.

30. An electron discharge device comprising: a cathode; an anode; said anode including a block of conducting material provided with a central bore receptive of said cathode; said block including a plurality of slots extending from said central bore to the exterior Wall thereof to form a plurality of electron-receiving portions separated by a plurality of primary cavity resonators; annular channel means connected to said block and cooperating with said exterior wall to form a secondary cavity resonator; and conducting rings at least partially closing opposite sides of said block; said primary cavity resonators opening into said secondary cavity resonator.

31. A electron discharge device comprising: an envelope enclosing a cathode and an anode structure; said anode structure including a plurality of anode elements forming a plurality of cavity resonators each of which is adapted to resonate at a predetermined output frequency; a common cavity resonator adapted to resonate at said predetermined output frequency; and a plurality of coupling devices coupled to said common cavity resonator; said coupling devices also being coupled, respectively, to some of said first-named cavity resonators which are spaced from each other by a distance equal to an integral number of wave length corresponding to said predetermined output frequency.

32. An electron discharge device having a hollow drum-shaped conducing member, a plurality of anode elements of sector-shaped transverse section mounted within said member in spaced relation thereto, whereby the inner wall of said drum-shaped member and the outer surface of said sector-shaped anode elements provide a cavity resonator, said anode element being spaced from each other along radial planes to provide radially-directed slots, the inner ends of said anode elements providing anode segments defining a cathode chamber, a cathode mounted in said chamber, said slots being resonant at the operating frequency of said device.

WILLIAM ERNEST WILLSHAW.

REFERENCES CITED The following references are of record in the file of this patent:

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